Hard Drive Data Recovery - A Basic Understanding of Platters

Hard disks can have one or more platters depending on their design. Normal consumer hard drives, most likely whats in your own PC, usually have between one and five platters. Some high-end drives, typically found in servers, can have as many as a dozen platters. Some very old drives had even more. In every hard drive, all the platters are actually linked together on a common central spindle, thus forming one single assembly that spins as one unit that is driven by the spindle motor. The platters are kept apart using spacer rings that fit over the spindle. The complete assembly is held from the top using a cap or cover and some screws.

Each platter has two surfaces that are able to hold data; each surface has a read/write head. Typically both surfaces of each platter are used, however that is not always true. Newer drives sometimes leave a surface vacant in order to create a drive of a particular capacity in a family of drives. With current drives holding vast amounts of data on a single platter, using only one surface of a platter allows for increased "granularity". Below is a table showing how Western Digital created five different capacities using three platters in their Caviar line of hard disk drives.

Hard drives with multiple platters are more challenging to manufacture due to the increased mass of the spindle unit, the need to accurately align all of the drives, as well as more complexity in keeping noise and vibration issues under control. More platters also mean increased mass resulting in slower response to commands to start or stop the drive; this can be compensated for with a stronger spindle motor which leads to other tradeoffs. Recently, the tendency has been towards hard drives with a smaller number of head arms and platters instead of more. The amount of data that can be stored on a given amount of hard disk platter space continues to increase, allowing the formation of large capacity drives without using lots of platters enabling manufacturers to decrease platter quantity and improve seek time without creating drives too small for the marketplace.

Another factor greatly the number of platters in a drive is the standard PC "slim line" hard disk form factor or external dimensions of the hard disk drive. This is limited to 1 inch in height therefore limiting the actual number of platters that can be placed in any single unit. Larger drives are often used in servers and generally hold many more platters than typical desktop PC hard drives. Naturally, engineers are continually working to decrease the amount of clearance needed between platters, thus increasing the number of platters in drives of any given height.